This study is designed to measure the production of neutron-induced DNA damage (strand breaks) in various lines of mammalian cells in tissue culture, and to examine the cells' ability to repair this damage under a variety of experimental conditions. The results with fast neutron will be contrasted with those obtained with 250 kvp x-rays. Parallel experiments in which cell survival is measured will allow comparison at the cellular and molecular levels. The results of this study will provide information about the cellular and molecular (DNA) effects of fast neutrons on mammalian cells. The data will provide estimates of the RBE and OER for fast neutrons using both molecular and cellular endpoints. The influence of various conditions such as cell type, cell age in the mitotic cycle, hypoxia, and treatment with various pharmacological radiation modifiers on the ability of neutron radiated cells to repair damage to their DNA, will provide insight into the basic mechanisms of neutron-induced cell inactivation.